1. Field of the Invention
This invention relates generally to computer displays and more particularly to a system and method for generating high-luminance windows on a computer display device.
2. Description of the Background Art
Optimal and effective presentation of visual information is a significant consideration of manufacturers, designers and users of computer display monitors. The use of computer displays for conveying various types of visual information is also becoming more important as computer system functionality increases. For example, a computer application may advantageously insert a separate viewing area or window onto a computer display screen. The window area may then display selected viewing information that is different from the viewing information presented on the display screen outside the window area. One such implementation displays video information from a video source (such as a video tape recorder) in the window area and simultaneously displays computer generated information (such as text or graphics) on the display screen outside the window area.
Referring now to FIG. 1, a diagram of a display 110 is shown. The display 110 includes a screen 112 that displays various types of viewing information to a system user. Display 110 includes a viewing window 114 which may be selectively sized and positioned on screen 112. A host computer system (not shown) may then advantageously insert selected video images within the video window 114 for viewing while the neighboring text and/or graphic information is simultaneously displayed on the remaining areas of screen 112.
In conventional computer displays that are not specifically designed for displaying video information, luminance levels are typically somewhat lower than the luminance levels used in conventional video displays. These lower luminance levels result in a relatively lower contrast ratio between dark and light areas of displayed information. In practice, window 114 is typically displayed at the same relative luminance levels as much of the surrounding screen 112 on display 110. However, lower luminance levels tend to produce video pictures which appear somewhat drab and washed-out. Conversely, higher luminance levels tend to bring out more detail in the displayed information and thus cause moving video images to appear more vivid and interesting to the viewer.
In operation, luminance levels are proportional to the amount of beam current generated in display 110. Higher luminance levels typically require greater beam current values. These increased beam currents, however, adversely affect the resolution of displayed information by increasing the spot size of the electron beam as it strikes phosphors lining the inner surface of screen 112. The increased spot size may result in a blurring of text or graphic information displayed on screen 112. Increasing beam current also may cause the cathode ray tube (CRT) of display 110 to unacceptably age at a faster degradation rate. Finally, the production of a higher beam current requires display 110 to dissipate a greater amount of power and therefore necessitates a heavier and more costly chassis when manufacturing display 110.
The foregoing factors (which are caused by increasing the luminance levels over the entire surface of screen 112) are undesirable in the design and manufacture of computer display monitors. Therefore, an improved system and method for generating high-luminance windows on a computer display device is needed, in accordance with the present invention.
In accordance with the present invention, a system and method are disclosed for generating high-luminance windows on a computer display device. In the preferred embodiment of the present invention, the computer display includes a video amplifier, a window generator, a high-voltage power supply (HVPS), an automatic beam limiter (ABL) and a cathode-ray tube (CRT). In the preferred embodiment, the video amplifier receives a video signal which includes information for presentation on the computer display. The video amplifier responsively amplifies the received video signal and then applies the amplified video signal to the cathode of the CRT. The HVPS provides a high-voltage signal to the anode of the CRT. The CRT responsively generates an electron beam which strikes phosphors located on the inner surface of the viewing screen of the CRT.
In the preferred embodiment, a processor device typically provides window control signals to the window generator in the computer display in response to a video application program running on a host computer system. The window control signals advantageously gate the generation of high-luminance windows on the computer display, in accordance with the present invention.
The window generator receives the window control signals and responsively generates and provides a window pulse to the ABL. The generated window pulse provides information about the size and position of the high-luminance windows on the viewing screen of the CRT. The ABL receives the window pulse and responsively generates and provides an analog window signal to the gain control of the video amplifier. The analog window signal thus increases the luminance of the amplified video signal during the period of the high-luminance window by increasing the gain of the video amplifier during the appropriate time period.
To prolong the life span of the computer display, the ABL also advantageously limits the average beam current provided to the CRT during the period of high-luminance window. In practice, the ABL samples beam current supplied by the HVPS. If the sampled beam current from the HVPS exceeds a preset threshold value, then the gain of the video amplifier is limited by adjusting the analog window signal. The present invention thus provides a video window with a higher luminance level than the remainder of the information displayed on the screen of the computer display and is therefore able to advantageously generate high-luminance windows on the computer display device.